libbpf: Support creating light skeleton of either endianness

Track target endianness in 'struct bpf_gen' and process in-memory data in
native byte-order, but on finalization convert the embedded loader BPF
insns to target endianness.

The light skeleton also includes a target-accessed data blob which is
heterogeneous and thus difficult to convert to target byte-order on
finalization. Add support functions to convert data to target endianness
as it is added to the blob.

Also add additional debug logging for data blob structure details and
skeleton loading.

Signed-off-by: Tony Ambardar <tony.ambardar@gmail.com>
Signed-off-by: Andrii Nakryiko <andrii@kernel.org>
Acked-by: Alexei Starovoitov <ast@kernel.org>
Link: https://lore.kernel.org/bpf/569562e1d5bf1cce80a1f1a3882461ee2da1ffd5.1726475448.git.tony.ambardar@gmail.com
Signed-off-by: Alexei Starovoitov <ast@kernel.org>

4 files changed, 139 insertions, 53 deletions

diff --git a/tools/lib/bpf/bpf_gen_internal.h b/tools/lib/bpf/bpf_gen_internal.h
index fdf44403ff36..6ff963a491d9 100644
--- a/tools/lib/bpf/bpf_gen_internal.h
+++ b/tools/lib/bpf/bpf_gen_internal.h
@@ -34,6 +34,7 @@ struct bpf_gen {
 	void *data_cur;
 	void *insn_start;
 	void *insn_cur;
+	bool swapped_endian;
 	ssize_t cleanup_label;
 	__u32 nr_progs;
 	__u32 nr_maps;
diff --git a/tools/lib/bpf/gen_loader.c b/tools/lib/bpf/gen_loader.c
index cf3323fd47b8..8a2b0f62d91d 100644
--- a/tools/lib/bpf/gen_loader.c
+++ b/tools/lib/bpf/gen_loader.c
@@ -401,6 +401,15 @@ int bpf_gen__finish(struct bpf_gen *gen, int nr_progs, int nr_maps)
 		opts->insns_sz = gen->insn_cur - gen->insn_start;
 		opts->data = gen->data_start;
 		opts->data_sz = gen->data_cur - gen->data_start;
+
+		/* use target endianness for embedded loader */
+		if (gen->swapped_endian) {
+			struct bpf_insn *insn = (struct bpf_insn *)opts->insns;
+			int insn_cnt = opts->insns_sz / sizeof(struct bpf_insn);
+
+			for (i = 0; i < insn_cnt; i++)
+				bpf_insn_bswap(insn++);
+		}
 	}
 	return gen->error;
 }
@@ -414,6 +423,28 @@ void bpf_gen__free(struct bpf_gen *gen)
 	free(gen);
 }
 
+/*
+ * Fields of bpf_attr are set to values in native byte-order before being
+ * written to the target-bound data blob, and may need endian conversion.
+ * This macro allows providing the correct value in situ more simply than
+ * writing a separate converter for *all fields* of *all records* included
+ * in union bpf_attr. Note that sizeof(rval) should match the assignment
+ * target to avoid runtime problems.
+ */
+#define tgt_endian(rval) ({					\
+	typeof(rval) _val = (rval);				\
+	if (gen->swapped_endian) {				\
+		switch (sizeof(_val)) {				\
+		case 1: break;					\
+		case 2: _val = bswap_16(_val); break;		\
+		case 4: _val = bswap_32(_val); break;		\
+		case 8: _val = bswap_64(_val); break;		\
+		default: pr_warn("unsupported bswap size!\n");	\
+		}						\
+	}							\
+	_val;							\
+})
+
 void bpf_gen__load_btf(struct bpf_gen *gen, const void *btf_raw_data,
 		       __u32 btf_raw_size)
 {
@@ -422,11 +453,12 @@ void bpf_gen__load_btf(struct bpf_gen *gen, const void *btf_raw_data,
 	union bpf_attr attr;
 
 	memset(&attr, 0, attr_size);
-	pr_debug("gen: load_btf: size %d\n", btf_raw_size);
 	btf_data = add_data(gen, btf_raw_data, btf_raw_size);
 
-	attr.btf_size = btf_raw_size;
+	attr.btf_size = tgt_endian(btf_raw_size);
 	btf_load_attr = add_data(gen, &attr, attr_size);
+	pr_debug("gen: load_btf: off %d size %d, attr: off %d size %d\n",
+		 btf_data, btf_raw_size, btf_load_attr, attr_size);
 
 	/* populate union bpf_attr with user provided log details */
 	move_ctx2blob(gen, attr_field(btf_load_attr, btf_log_level), 4,
@@ -457,28 +489,29 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 	union bpf_attr attr;
 
 	memset(&attr, 0, attr_size);
-	attr.map_type = map_type;
-	attr.key_size = key_size;
-	attr.value_size = value_size;
-	attr.map_flags = map_attr->map_flags;
-	attr.map_extra = map_attr->map_extra;
+	attr.map_type = tgt_endian(map_type);
+	attr.key_size = tgt_endian(key_size);
+	attr.value_size = tgt_endian(value_size);
+	attr.map_flags = tgt_endian(map_attr->map_flags);
+	attr.map_extra = tgt_endian(map_attr->map_extra);
 	if (map_name)
 		libbpf_strlcpy(attr.map_name, map_name, sizeof(attr.map_name));
-	attr.numa_node = map_attr->numa_node;
-	attr.map_ifindex = map_attr->map_ifindex;
-	attr.max_entries = max_entries;
-	attr.btf_key_type_id = map_attr->btf_key_type_id;
-	attr.btf_value_type_id = map_attr->btf_value_type_id;
-
-	pr_debug("gen: map_create: %s idx %d type %d value_type_id %d\n",
-		 attr.map_name, map_idx, map_type, attr.btf_value_type_id);
+	attr.numa_node = tgt_endian(map_attr->numa_node);
+	attr.map_ifindex = tgt_endian(map_attr->map_ifindex);
+	attr.max_entries = tgt_endian(max_entries);
+	attr.btf_key_type_id = tgt_endian(map_attr->btf_key_type_id);
+	attr.btf_value_type_id = tgt_endian(map_attr->btf_value_type_id);
 
 	map_create_attr = add_data(gen, &attr, attr_size);
-	if (attr.btf_value_type_id)
+	pr_debug("gen: map_create: %s idx %d type %d value_type_id %d, attr: off %d size %d\n",
+		 map_name, map_idx, map_type, map_attr->btf_value_type_id,
+		 map_create_attr, attr_size);
+
+	if (map_attr->btf_value_type_id)
 		/* populate union bpf_attr with btf_fd saved in the stack earlier */
 		move_stack2blob(gen, attr_field(map_create_attr, btf_fd), 4,
 				stack_off(btf_fd));
-	switch (attr.map_type) {
+	switch (map_type) {
 	case BPF_MAP_TYPE_ARRAY_OF_MAPS:
 	case BPF_MAP_TYPE_HASH_OF_MAPS:
 		move_stack2blob(gen, attr_field(map_create_attr, inner_map_fd), 4,
@@ -498,8 +531,8 @@ void bpf_gen__map_create(struct bpf_gen *gen,
 	/* emit MAP_CREATE command */
 	emit_sys_bpf(gen, BPF_MAP_CREATE, map_create_attr, attr_size);
 	debug_ret(gen, "map_create %s idx %d type %d value_size %d value_btf_id %d",
-		  attr.map_name, map_idx, map_type, value_size,
-		  attr.btf_value_type_id);
+		  map_name, map_idx, map_type, value_size,
+		  map_attr->btf_value_type_id);
 	emit_check_err(gen);
 	/* remember map_fd in the stack, if successful */
 	if (map_idx < 0) {
@@ -784,12 +817,12 @@ log:
 	emit_ksym_relo_log(gen, relo, kdesc->ref);
 }
 
-static __u32 src_reg_mask(void)
+static __u32 src_reg_mask(struct bpf_gen *gen)
 {
-#if defined(__LITTLE_ENDIAN_BITFIELD)
-	return 0x0f; /* src_reg,dst_reg,... */
-#elif defined(__BIG_ENDIAN_BITFIELD)
-	return 0xf0; /* dst_reg,src_reg,... */
+#if defined(__LITTLE_ENDIAN_BITFIELD) /* src_reg,dst_reg,... */
+	return gen->swapped_endian ? 0xf0 : 0x0f;
+#elif defined(__BIG_ENDIAN_BITFIELD) /* dst_reg,src_reg,... */
+	return gen->swapped_endian ? 0x0f : 0xf0;
 #else
 #error "Unsupported bit endianness, cannot proceed"
 #endif
@@ -840,7 +873,7 @@ static void emit_relo_ksym_btf(struct bpf_gen *gen, struct ksym_relo_desc *relo,
 	emit(gen, BPF_JMP_IMM(BPF_JA, 0, 0, 3));
 clear_src_reg:
 	/* clear bpf_object__relocate_data's src_reg assignment, otherwise we get a verifier failure */
-	reg_mask = src_reg_mask();
+	reg_mask = src_reg_mask(gen);
 	emit(gen, BPF_LDX_MEM(BPF_B, BPF_REG_9, BPF_REG_8, offsetofend(struct bpf_insn, code)));
 	emit(gen, BPF_ALU32_IMM(BPF_AND, BPF_REG_9, reg_mask));
 	emit(gen, BPF_STX_MEM(BPF_B, BPF_REG_8, BPF_REG_9, offsetofend(struct bpf_insn, code)));
@@ -931,48 +964,94 @@ static void cleanup_relos(struct bpf_gen *gen, int insns)
 	cleanup_core_relo(gen);
 }
 
+/* Convert func, line, and core relo info blobs to target endianness */
+static void info_blob_bswap(struct bpf_gen *gen, int func_info, int line_info,
+			    int core_relos, struct bpf_prog_load_opts *load_attr)
+{
+	struct bpf_func_info *fi = gen->data_start + func_info;
+	struct bpf_line_info *li = gen->data_start + line_info;
+	struct bpf_core_relo *cr = gen->data_start + core_relos;
+	int i;
+
+	for (i = 0; i < load_attr->func_info_cnt; i++)
+		bpf_func_info_bswap(fi++);
+
+	for (i = 0; i < load_attr->line_info_cnt; i++)
+		bpf_line_info_bswap(li++);
+
+	for (i = 0; i < gen->core_relo_cnt; i++)
+		bpf_core_relo_bswap(cr++);
+}
+
 void bpf_gen__prog_load(struct bpf_gen *gen,
 			enum bpf_prog_type prog_type, const char *prog_name,
 			const char *license, struct bpf_insn *insns, size_t insn_cnt,
 			struct bpf_prog_load_opts *load_attr, int prog_idx)
 {
+	int func_info_tot_sz = load_attr->func_info_cnt *
+			       load_attr->func_info_rec_size;
+	int line_info_tot_sz = load_attr->line_info_cnt *
+			       load_attr->line_info_rec_size;
+	int core_relo_tot_sz = gen->core_relo_cnt *
+			       sizeof(struct bpf_core_relo);
 	int prog_load_attr, license_off, insns_off, func_info, line_info, core_relos;
 	int attr_size = offsetofend(union bpf_attr, core_relo_rec_size);
 	union bpf_attr attr;
 
 	memset(&attr, 0, attr_size);
-	pr_debug("gen: prog_load: type %d insns_cnt %zd progi_idx %d\n",
-		 prog_type, insn_cnt, prog_idx);
 	/* add license string to blob of bytes */
 	license_off = add_data(gen, license, strlen(license) + 1);
 	/* add insns to blob of bytes */
 	insns_off = add_data(gen, insns, insn_cnt * sizeof(struct bpf_insn));
+	pr_debug("gen: prog_load: prog_idx %d type %d insn off %d insns_cnt %zd license off %d\n",
+		 prog_idx, prog_type, insns_off, insn_cnt, license_off);
 
-	attr.prog_type = prog_type;
-	attr.expected_attach_type = load_attr->expected_attach_type;
-	attr.attach_btf_id = load_attr->attach_btf_id;
-	attr.prog_ifindex = load_attr->prog_ifindex;
-	attr.kern_version = 0;
-	attr.insn_cnt = (__u32)insn_cnt;
-	attr.prog_flags = load_attr->prog_flags;
-
-	attr.func_info_rec_size = load_attr->func_info_rec_size;
-	attr.func_info_cnt = load_attr->func_info_cnt;
-	func_info = add_data(gen, load_attr->func_info,
-			     attr.func_info_cnt * attr.func_info_rec_size);
+	/* convert blob insns to target endianness */
+	if (gen->swapped_endian) {
+		struct bpf_insn *insn = gen->data_start + insns_off;
+		int i;
 
-	attr.line_info_rec_size = load_attr->line_info_rec_size;
-	attr.line_info_cnt = load_attr->line_info_cnt;
-	line_info = add_data(gen, load_attr->line_info,
-			     attr.line_info_cnt * attr.line_info_rec_size);
+		for (i = 0; i < insn_cnt; i++, insn++)
+			bpf_insn_bswap(insn);
+	}
 
-	attr.core_relo_rec_size = sizeof(struct bpf_core_relo);
-	attr.core_relo_cnt = gen->core_relo_cnt;
-	core_relos = add_data(gen, gen->core_relos,
-			     attr.core_relo_cnt * attr.core_relo_rec_size);
+	attr.prog_type = tgt_endian(prog_type);
+	attr.expected_attach_type = tgt_endian(load_attr->expected_attach_type);
+	attr.attach_btf_id = tgt_endian(load_attr->attach_btf_id);
+	attr.prog_ifindex = tgt_endian(load_attr->prog_ifindex);
+	attr.kern_version = 0;
+	attr.insn_cnt = tgt_endian((__u32)insn_cnt);
+	attr.prog_flags = tgt_endian(load_attr->prog_flags);
+
+	attr.func_info_rec_size = tgt_endian(load_attr->func_info_rec_size);
+	attr.func_info_cnt = tgt_endian(load_attr->func_info_cnt);
+	func_info = add_data(gen, load_attr->func_info, func_info_tot_sz);
+	pr_debug("gen: prog_load: func_info: off %d cnt %d rec size %d\n",
+		 func_info, load_attr->func_info_cnt,
+		 load_attr->func_info_rec_size);
+
+	attr.line_info_rec_size = tgt_endian(load_attr->line_info_rec_size);
+	attr.line_info_cnt = tgt_endian(load_attr->line_info_cnt);
+	line_info = add_data(gen, load_attr->line_info, line_info_tot_sz);
+	pr_debug("gen: prog_load: line_info: off %d cnt %d rec size %d\n",
+		 line_info, load_attr->line_info_cnt,
+		 load_attr->line_info_rec_size);
+
+	attr.core_relo_rec_size = tgt_endian((__u32)sizeof(struct bpf_core_relo));
+	attr.core_relo_cnt = tgt_endian(gen->core_relo_cnt);
+	core_relos = add_data(gen, gen->core_relos, core_relo_tot_sz);
+	pr_debug("gen: prog_load: core_relos: off %d cnt %d rec size %zd\n",
+		 core_relos, gen->core_relo_cnt,
+		 sizeof(struct bpf_core_relo));
+
+	/* convert all info blobs to target endianness */
+	if (gen->swapped_endian)
+		info_blob_bswap(gen, func_info, line_info, core_relos, load_attr);
 
 	libbpf_strlcpy(attr.prog_name, prog_name, sizeof(attr.prog_name));
 	prog_load_attr = add_data(gen, &attr, attr_size);
+	pr_debug("gen: prog_load: attr: off %d size %d\n",
+		 prog_load_attr, attr_size);
 
 	/* populate union bpf_attr with a pointer to license */
 	emit_rel_store(gen, attr_field(prog_load_attr, license), license_off);
@@ -1040,7 +1119,6 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
 	int zero = 0;
 
 	memset(&attr, 0, attr_size);
-	pr_debug("gen: map_update_elem: idx %d\n", map_idx);
 
 	value = add_data(gen, pvalue, value_size);
 	key = add_data(gen, &zero, sizeof(zero));
@@ -1068,6 +1146,8 @@ void bpf_gen__map_update_elem(struct bpf_gen *gen, int map_idx, void *pvalue,
 	emit(gen, BPF_EMIT_CALL(BPF_FUNC_probe_read_kernel));
 
 	map_update_attr = add_data(gen, &attr, attr_size);
+	pr_debug("gen: map_update_elem: idx %d, value: off %d size %d, attr: off %d size %d\n",
+		 map_idx, value, value_size, map_update_attr, attr_size);
 	move_blob2blob(gen, attr_field(map_update_attr, map_fd), 4,
 		       blob_fd_array_off(gen, map_idx));
 	emit_rel_store(gen, attr_field(map_update_attr, key), key);
@@ -1084,14 +1164,16 @@ void bpf_gen__populate_outer_map(struct bpf_gen *gen, int outer_map_idx, int slo
 	int attr_size = offsetofend(union bpf_attr, flags);
 	int map_update_attr, key;
 	union bpf_attr attr;
+	int tgt_slot;
 
 	memset(&attr, 0, attr_size);
-	pr_debug("gen: populate_outer_map: outer %d key %d inner %d\n",
-		 outer_map_idx, slot, inner_map_idx);
 
-	key = add_data(gen, &slot, sizeof(slot));
+	tgt_slot = tgt_endian(slot);
+	key = add_data(gen, &tgt_slot, sizeof(tgt_slot));
 
 	map_update_attr = add_data(gen, &attr, attr_size);
+	pr_debug("gen: populate_outer_map: outer %d key %d inner %d, attr: off %d size %d\n",
+		 outer_map_idx, slot, inner_map_idx, map_update_attr, attr_size);
 	move_blob2blob(gen, attr_field(map_update_attr, map_fd), 4,
 		       blob_fd_array_off(gen, outer_map_idx));
 	emit_rel_store(gen, attr_field(map_update_attr, key), key);
@@ -1112,8 +1194,9 @@ void bpf_gen__map_freeze(struct bpf_gen *gen, int map_idx)
 	union bpf_attr attr;
 
 	memset(&attr, 0, attr_size);
-	pr_debug("gen: map_freeze: idx %d\n", map_idx);
 	map_freeze_attr = add_data(gen, &attr, attr_size);
+	pr_debug("gen: map_freeze: idx %d, attr: off %d size %d\n",
+		 map_idx, map_freeze_attr, attr_size);
 	move_blob2blob(gen, attr_field(map_freeze_attr, map_fd), 4,
 		       blob_fd_array_off(gen, map_idx));
 	/* emit MAP_FREEZE command */
diff --git a/tools/lib/bpf/libbpf.c b/tools/lib/bpf/libbpf.c
index 041228674bfa..712b95e8891b 100644
--- a/tools/lib/bpf/libbpf.c
+++ b/tools/lib/bpf/libbpf.c
@@ -9134,6 +9134,7 @@ int bpf_object__gen_loader(struct bpf_object *obj, struct gen_loader_opts *opts)
 	if (!gen)
 		return -ENOMEM;
 	gen->opts = opts;
+	gen->swapped_endian = !is_native_endianness(obj);
 	obj->gen_loader = gen;
 	return 0;
 }
diff --git a/tools/lib/bpf/skel_internal.h b/tools/lib/bpf/skel_internal.h
index 0875452521e9..4d5fa079b5d6 100644
--- a/tools/lib/bpf/skel_internal.h
+++ b/tools/lib/bpf/skel_internal.h
@@ -351,10 +351,11 @@ static inline int bpf_load_and_run(struct bpf_load_and_run_opts *opts)
 	attr.test.ctx_size_in = opts->ctx->sz;
 	err = skel_sys_bpf(BPF_PROG_RUN, &attr, test_run_attr_sz);
 	if (err < 0 || (int)attr.test.retval < 0) {
-		opts->errstr = "failed to execute loader prog";
 		if (err < 0) {
+			opts->errstr = "failed to execute loader prog";
 			set_err;
 		} else {
+			opts->errstr = "error returned by loader prog";
 			err = (int)attr.test.retval;
 #ifndef __KERNEL__
 			errno = -err;